1. Field of the Invention
This invention pertains generally to an apparatus for controlling water-based liquid waste and, more particularly, to an apparatus which employs a vacuum distillation vessel for separating water-based liquid waste into a pure, distilled water component and a waste sludge component.
2. Description of the Background Art
Due to increasingly stringent worldwide environmental laws pertaining to the handling and discharge of liquid waste materials, the design of new, highly efficient, liquid waste treatment devices are of critical importance. In the interest of conforming to new laws in this area, the manufacturing and processing services industry has experienced increased costs of operation and, increasingly, fines have been levied against industries for not meeting the standards set by the new laws.
A sampling of the industries affected by these increasingly stringent environmental laws include industries involved in photography, metal plating, printing, ink manufacturing, paint manufacturing, paper manufacturing, cosmetics, food processing, mining, mechanical, and other industries. A common aspect of the liquid waste streams which emanate from these types of industries, is that the wastes involved generally possess a high water composition, having dissolved solutes/waste therein, which makes it possible for devices to be applied to the liquid waste stream which separate the water fraction from the dissolved solute/waste fraction. By separating out and purifying the water fraction, the water can ideally be released into a municipal sewer system, and the dissolved solute/waste fraction can be concentrated into a sufficiently pumpable sludge component, for purposes of chemical recovery and/or subsequent disposal.
Currently used devices for separating water-based liquid waste into a dissolved solute fraction, and a substantially pure water fraction, generally involve the use of a vacuum distillation vessel. The typical vacuum distillation device operates by providing a low pressure atmosphere within the distillation vessel for achieving low temperature boiling of the raw, original, liquid waste solution. The low pressure atmosphere is generally maintained by a vacuum pump coupled to the vacuum distillation vessel. A refrigeration system provides a refrigeration circuit, consisting of a heat pump for heating the original liquid waste solution to boiling temperature, and a chiller for condensing water from vapor. The heat pump side of the refrigeration system functions by routing hot compressed freon gas through a heat exchanger, which provides the heat necessary for low temperature boiling of the original liquid waste solution. The chiller side of the refrigeration system is coupled to one or more condenser coils, which provide a cool surface within the vacuum distillation vessel, for condensing evaporated water resulting from boiling the liquid waste solution.
The refrigeration system used in a typical vacuum distillation device having a 1,600 gallon per day capacity, requires the use of a large compressor in the 44-horsepower range. This large compressor is required to keep the heat pump at a functioning level, during the start up cycle, while the chiller side of the refrigeration system comes up to a functioning level, to begin cooling. During start up, the temperature of the original liquid waste solution is brought up to a boiling level, through the operation of the heat pump. During this time, the chiller is not functioning at full capacity, so a "false load" must be created by the compressor to compensate, until the chiller side begins operating at a fully functional level. Without this "false load" applied by the compressor, the refrigeration system would cease to operate. The huge energy demand of such a large compressor, coupled with the mechanical complexity required in such a system, to facilitate the start up procedure, represents a significant drawback to this type of vacuum distillation device.
Once the refrigeration circuit is started, and the boiling process is underway, the water portion of the original liquid waste solution separates, and travels upward within the vacuum distillation vessel, in vapor form, until it contacts the cool condenser coils. Upon condensing, the water is in a distilled form having a residual dissolved solute concentration in the range of 2000 parts per million (ppm). This distilled water is subsequently pumped from the distillation vessel into a holding tank. The remaining solute fraction continues to undergo the boiling process within the vacuum distillation vessel, until enough water is removed, to concentrate the solute fraction to a pumpable sludge having a specific gravity of around 1.4. This sludge is then drained out of the vessel, and subsequently subjected to materials recovery methods and/or disposed of.
Due to increasingly stringent environmental laws around the world, it has become apparent that the 2000 ppm residual solute level achieved by current vacuum distillation devices is at a dissolved solute level considered by many standards to be too high for direct discharge into municipal sewer systems. Hence, additional treatment by a variety of separate methods is often required before the distilled water is pure enough for direct discharge.
It is also highly desirable in some industries to have a waste treatment apparatus which can separate the water component from the liquid waste solution, and treat it to a purity level high enough for reuse within the industrial facility, where it originated. By having water available for reuse, the relevant industry will be able to have pure water available for use in chemistry and other processes.
Moreover, current vacuum distillation devices suffer from a lack of evaporative efficiency, such that it often takes an excessively long time for the water component in a defined volume of the original liquid waste solution to completely separate from the solute component, such that the solute component is finally reduced to a pumpable sludge having a specific gravity of around 1.4.
Another desirable feature lacking in current vacuum distillation devices involves controlling the escape of hazardous gasses from the original liquid waste solution. This problem is especially prevalent in photo-chemical waste processing. Water-based photo-chemical wastes contain a high degree of dissolved silver, and additionally, contain dissolved ammonium sulfate. The silver is easily removed by a silver recovery unit, but the dissolved ammonium sulfate creates a significant health and safety problem, by releasing from the original photo-chemical waste solution in the form of a gas. This ammonium sulfate gas can leak from the vacuum distillation vessel and/or waste holding tank, and upon being inhaled by humans, can cause significant ill effects. It is therefore desirable to have a vacuum distillation device which prevents the leakage of hazardous gasses, such as ammonium sulfate.
Additionally, it is desirable for a vacuum distillation device to operate as economically as possible. If such a device uses more energy than needed to evaporate the original liquid waste solution, this translates into added costs to the business sector. Hence, new designs are constantly being sought to make vacuum distillation devices as economical and as energy-efficient as possible.
Another problem inherent in current vacuum distillation devices is the problem of controlling the growth of microorganisms and algae in the distilled water component after it leaves the vacuum distillation vessel, and is stored in a holding tank. These microorganisms and algae are collectively called "bio-slime" and their existence significantly downgrades the purity of the distilled water component, as well as creates problems by clogging pipes, valves and other mechanical components of the typical vacuum distillation device. Current methods of bio-slime control involves adding chemicals to the distilled water storage tank, to retard their growth. However, by adding chemicals, the purity of the distilled water is downgraded, further.
In summary, known vacuum distillation devices have become increasingly unable to achieve the levels of distilled water purity which comply with current and future environmental standards. Normal residual dissolved solute contamination in the distilled water component, coupled with bio-slime growth, and introduced chemicals to control such growth, have resulted in the distilled water component being too contaminated to be released directly into municipal sewers, or available for reuse, without additional treatment. It has also become necessary to provide a waste treatment apparatus which controls the escape of hazardous gasses. Additionally, business economics have dictated that a more energy efficient vacuum distillation device be developed. The present invention successfully overcomes the deficiencies inherent in current vacuum distillation devices by providing a waste treatment apparatus based on a vacuum distillation device, having increased evaporative efficiency, that is both economical and compliant with modern environmental laws.
The foregoing discussion reflects the state of the art of which the applicant is aware and is tendered with a view toward discharging applicant's acknowledged duty of candor in disclosing information which may be pertinent to the examination of this application.